Seafloor Microscope Zooms In on Tiniest Bits of Coral

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An underwater microscope that divers can use to view corals on the seafloor can show details down to one micron, or one-hundredth the width of a human hair.Published OnJuly 12, 2016CreditImage by Scripps Institution of Oceanography/University of California, San Diego

Coral reefs can extend more than 1,000 miles, but they are made by coral polyps as small as one sixteenth of an inch.

These creatures don’t move about as adults. “Think upside down jellyfish stuck to a rock,” said Andrew D. Mullen, a graduate student at the Scripps Institution of Oceanography at the University of California, San Diego.

Mr. Mullen, Tali Treibitz and other American and Israeli scientists built a new microscope to study corals in nature while he and Dr. Treibitz, now running a lab at the University of Haifa, were both working in the lab of Jules S. Jaffe at Scripps.

As they report in Nature Communications, this is the first microscope made for use on the seafloor that is powerful enough to show details, almost as small as one micron, of living corals in their natural state.

Divers can use the system, which includes a flexible lens for focusing and does not disturb the corals, since it can be placed a couple of inches away from them.

They developed the tool to study what happens during coral bleaching and its aftermath.

Although corals are animals, they also contain single-cell organisms called zooxanthellae that can photosynthesize, enabling the corals to share in energy captured directly from the sun.

Coral bleaching occurs when warm temperatures cause the polyps to expel the zooxanthellae, leaving them colorless. The microscope is powerful enough to show individual zooxanthellae, about 10 microns, or one-tenth the width of a human hair, in the polyps.

In this weakened state, the reefs are often colonized by algae, and the microscope may show how this happens.

In trial runs of the microscope in the Red Sea, the scientists recorded video of corals in conflict. They moved a loose block of coral that had broken off and was lying on the seafloor next to coral of a different species.

The much-speeded-up video shows the polyps of one species engaging the others by extending their digestive systems like an attacking amoeba to digest the invaders.

The researchers have also recorded more friendly interactions within a species in which the corals look as if they are kissing.

In reality they seem to be exchanging food, Mr. Mullen said.

But that’s friendly, too.

Correction:

An earlier version of this article misstated the size of coral polyps. They can be as small as one-sixteenth of an inch, not 10 microns.

A version of this article appears in print on , on Page D2 of the New York edition with the headline: Sciencetake: Seafloor Microscope Gives Scientists Look at the Lives of Corals. Order Reprints | Today’s Paper | Subscribe